Preheat oven to 450 F. Move the rack to the middle of the oven. Line a large baking sheet with parchment paper.: As the oven hums to temperature you will notice the kitchen air warm and the oven light glow, signaling readiness. Lining the pan with parchment prevents sticking and makes cleanup effortless, and placing the rack in the middle ensures even heat circulation so the bok choy gets uniform color. The high heat is essential to encourage quick caramelization rather than slow steaming, which preserves crispness. A common mistake is using a cold pan, which delays browning, so always let the oven fully reach temperature before you slide the sheet in. If your oven runs hot, watch the first batch closely to avoid overdarkening.
Cut the baby bok choy in half lengthwise and trim the dry ends if needed (the white part). Place the baby bok choy on the baking sheet. Pour olive oil on both sides of each piece of bok choy (and rub it in), then grind some pepper on each piece too. I like to roast it face-down first. Place the baking sheet in the oven and roast for 5 minutes/side (it will be tender-crisp with some crispy leaves). If you want it done more, roast it a little longer.: You will see the pale stems and green leaves reveal a clean cut surface that will brown beautifully when exposed to heat. Trimming the dry ends improves presentation and removes woody bits that do not soften as quickly. Arrange the halves with the cut side slightly exposed to heat, which maximizes browning on the stems while letting the leaves crisp at the edges. A frequent oversight is overcrowding the pan, which traps steam and prevents crisping, so give each piece breathing room.
Meanwhile, whisk the soy sauce, lemon juice, garlic powder, and red pepper flakes together in a small bowl.: As you rub olive oil into the surface, it glistens and highlights the veins of the leaves; the oil also acts as a heat conductor that promotes those pretty browned tips. The cracked pepper will toast slightly in the oven, adding a toasted spice note. Ensure a thin, even coat of oil rather than drowning the vegetable, because excess oil can pool and slow crisping. Avoid skipping the rub step, as uneven oiling leads to patchy browning.
Once the baby bok choy is done to your liking, drizzle the sauce on each piece. Serve immediately.: Placing the bok choy cut side down against the sheet produces a concentrated sear on the stem, which yields a sweeter, caramelized flavor and a satisfying contrast with the leafy tops. You will hear a faint sizzle as the oil meets the hot pan, and after a few minutes the edge will begin to darken and char slightly, which is the visual cue to flip if you choose to. One mistake people make is leaving pieces face-up, which reduces direct contact with the hot surface and limits browning.
Place the baking sheet in the oven and roast for 5 minutes/side (it will be tender-crisp with some crispy leaves). If you want it done more, roast it a little longer.: Near the five minute mark you will notice the stems turning translucent with the slightest golden edges and the leaves blistering at the tips, releasing an aroma that is vegetal, nutty, and faintly sweet. That tender crispness is the goal, where the stems yield a bite but still hold texture. If you prefer softer stems, add a minute or two, but watch closely because the leaves can go from blistered to burnt quickly. Avoid overcooking, which produces limp, flavorless greens.
Meanwhile, whisk the soy sauce, lemon juice, garlic powder, and red pepper flakes together in a small bowl.: As you whisk the glossy sauce, the citrus scent lifts and the soy sauce tames with a salty umami depth, while garlic powder adds roundness and the red pepper flakes introduce warmth. The texture should be smooth and slightly thin so it can be drizzled easily; if it seems too viscous, a tiny splash of water will loosen it. Mixing while the bok choy roasts ensures the sauce is fresh and bright when you finish. A common slip is making the sauce too heavy handed in salt, so taste and adjust before drizzling.
Once the baby bok choy is done to your liking, drizzle the sauce on each piece. Serve immediately.: The final drizzle brings the dish together, and you will hear the faint hiss as the sauce meets the hot surface and releases aromatics, and the lemon will sparkle against the roasted sugars. Serve right away so the contrast between warm stems and crisp leaves is preserved, and watch how the glossy sauce clings to the textures. A typical error is letting the bok choy sit too long after saucing, which softens the crisp edges and dulls the initial brightness, so plate and pass quickly.