Preheat the oven to 400 degrees F. Set out a large rimmed baking sheet with parchment paper.: When you open the oven and slide the sheet in, you should hear a faint hiss as the hot air meets the metal, and that initial high heat is what encourages the beets to begin caramelizing right away. Preheating also ensures even cooking, because putting beets into a cold oven will cause them to steam and become mushy instead of developing browned edges. A common mistake is not preheating fully, which leads to longer cook time and uneven color. Make sure the rack is centered so the heat circulates around the pan well.
To a large bowl, add diced beets, drizzle with olive oil, and sprinkle with sea salt. Mix together until all ingredients are integrated. Add beets to the sheet pan in a flat layer.: As you toss the beets with olive oil and sea salt , smell the faintly fruity oil and the mineral salt coating each cube. The oil acts as a conductor for heat and helps promote browning, while the salt draws out moisture and amplifies sweetness. Spread the pieces in a single layer so air can circulate and each side can brown. Overcrowding the pan traps steam, preventing crisping, which is a frequent error. Use two pans if necessary to give the beets space to roast.
Add beets to the oven. How long to roast beets in oven will vary a bit based on size of the chunks. My technique is to bake beets for 15 minutes. Flip them around with a spatula and bake for another 5-10 minutes or as long as desired until beets roast to your desired level of doneness. They should be fork tender and starting to brown around the edges.: Inside the oven you will notice aromas start to deepen after about 10 to 12 minutes, as sugars start to caramelize. I aim to bake the beets for 15 minutes, then flip them and continue roasting for another 5 to 10 minutes until they are fork tender and edges show browning. The sound is subtle, mostly the quiet crackle of roasted sugars, and visually you want to see color developing on several sides. The rationale for this two stage timing is to give them an initial blast of heat to set surface color, then even out doneness after flipping. A typical mistake is leaving them untouched for the whole roast, which can cause uneven browning and some pieces to overcook while others remain firm.
Transfer oven roasted beets to a serving platter and sprinkle with parsley and goat cheese crumbles or squares, a crack of salt and pepper as desired, pumpkin seeds, and (optional) a squeeze of lemon juice.: When you flip the beets , you should see areas that have taken on deep mahogany edges while other faces are still lighter, and this is the cue they need another short stint in the oven. The flip helps each side get exposure to the hot pan surface, increasing even caramelization and developing a mix of tender insides and slightly crisped outsides. If you skip flipping, the bottoms may become too dark while tops stay underdone. Watch for fork tenderness as your primary indicator rather than exact times, because oven temperatures and cubing size vary widely.
Transfer oven roasted beets to a serving platter and sprinkle with parsley and goat cheese crumbles or squares, a crack of salt and pepper as desired, pumpkin seeds, and optional squeeze of lemon juice.: As you move the warm beets to the platter, you will notice the steam rising and the sweet, concentrated aroma that built during roasting. Scatter the chopped parsley to add a fresh green contrast, and crumble the goat cheese so pockets of creamy tang melt slightly against the warm cubes. The toasted pumpkin seeds add a satisfying snap, and a tiny squeeze of lemon juice brightens the whole ensemble. Avoid adding too much acid, which can overwhelm the delicate balance, and taste before adding a final pinch of sea salt or more pepper .