Melt the coconut oil in a large skillet over medium-high heat. Add the onions and a pinch of salt. Stir to combine. Reduce heat to medium-low and cook, stirring occasionally, until onions are golden and soft, about 20-30 minutes. While the onions cook, prep the rest of the ingredients.

Once the onions are ready, stir in the carrots and peppers. Add 1 tablespoon water and increase the heat to medium. Cover and cook, stirring occasionally, until tender, about 6-8 minutes. Add the corn and garlic and cook, stirring, 1-2 minutes. Add the cumin, cinnamon, allspice and cayenne cook 1 minute. Remove from heat. Stir in the lemon juice and cilantro. Season to taste with sea salt. Spread the filling out on a plate and let cool (feel free to stick it in the fridge to cool it faster). Do Ahead: The filling can be refrigerated in a sealed container overnight.

Preheat the oven to 400˚F. Line a large baking sheet with parchment paper.

In a small bowl, whisk the egg with 1 teaspoon of water to make an egg wash.

Roll out the dough on a piece of wax paper, using amaranth flour for dusting as needed, to a 12-inch round. Flip onto the baking sheet and peel off the wax paper. Brush with egg wash. Spread the vegetable filling in the center, leaving a 1-2-inch border. Fold and pinch the sides of the dough over the filling to make a rustic crostada. The dough will crack a bit as you fold it; just pinch and patch it back together as needed. Brush the outside with egg wash. Do Ahead: At this point the tart can be refrigerated, uncovered, for up to 1 hour.