Preheat oven to 375˚F | 190°C.: When you open the oven and warm air meets the kitchen, there is a subtle wave of readiness that sets the tone. The heat priming creates an environment where the topping will brown evenly and the fruit will start to bubble on schedule. You should feel the oven climb and hear the faint hum of its element engaging. If your oven runs hot or cool, use an oven thermometer to confirm actual temperature, because an off oven can burn the topping before the filling bubbles. A common mistake is skipping preheating, which leads to longer baking and uneven texture.
Combine strawberries, rhubarb, sugar (or sweetener), cornstarch (corn flour) and vanilla in a 2-quart 8-inch baking dish. Mix well to evenly coat.: The first sensory cue is the scent of vanilla lifting as you stir the glossy fruit, and you will notice the sugar drawing liquid from the strawberries and rhubarb . The cornstarch should disappear into the syrupy mixture, leaving no visible specks. Mixing thoroughly ensures each piece is coated so the filling thickens uniformly while baking. If you under-mix, pockets of dry cornstarch or uneven sweetness can result. One problem to avoid is overcrowding the dish; if fruit is piled too tightly, it steams rather than bakes and prevents evaporation needed for a syrupy finish.
In a medium-sized bowl, combine the oats, flour (or almond meal), coconut, honey, butter (or oil), sugar and salt together. Mix well.: As you combine these dry and wet elements, the aroma of toasted coconut and brown sugar mingling with melted butter or coconut oil becomes compelling. The mixture should form loose clusters as the honey and fat bind the oats and flour. Those clusters toast into crunchy bits when baked. Stir until the ingredients are evenly moistened, but avoid overworking which can create a paste like texture. A common mistake is adding too much fat, which yields a greasy topping instead of crisp shards.
Evenly cover the fruit with the oat mixture and bake for 45 minutes, or until the fruit starts to bubble and the crumble is golden and crisp. Serve immediately with ice cream, frozen yogurt, or plain.: When the dish goes into the oven, expect a quiet sizzling to begin as juices heat up, and after about 30 minutes you will see gentle bubbling at the edges. The topping should turn a deep golden and you may hear faint crackles as oats crisp. The smell will shift from raw ingredients to warm caramel and baked fruit, filling the kitchen with an irresistible scent. The bubbling indicates the cornstarch has activated to thicken the juices into a syrup consistency. Avoid opening the oven repeatedly, which lowers internal temperature and can prevent proper browning. If the topping browns too fast before the filling bubbles, tent with foil to slow surface browning while the filling finishes cooking. When done, allow a short rest so the filling sets slightly, then serve warm for ideal texture contrast and aroma.