Preheat the oven to 400°F;
In a sauté pan, fry off the onions with a drizzle of olive oil until soft and slightly caramelized, about 4 - 5 minutes, then add in the garlic, cook till aromatic;
Add in the broccoli, cauliflower, and carrots, cook till soft, add in the mushrooms, cook till they let out moisture, then season with the balsamic vinegar and coconut amino;
Stir in the baby spinach, cook till just wilted, add a pinch of salt and black pepper to taste, remove from heat and set aside;
In a big mixing bowl, use a hand blender to blend together all the "egg" mixture ingredients until very smooth or pulse in a food processor till smooth;
Fold in the sautéed vegetables, stir to combine evenly;
Slice the zucchini and tomatoes into 1/4 inch thick rounds, then cut the rounds into halves;
Carve out the white part of the zucchini, use only the green crescent part, and fit the tomato halves into the zucchini greens;
Put one parchment paper cupcake liner into each cupcake pan space, and fill each cup with the quiche mixture till it's level with the rim, you can use an ice cream scooper to make this part neater;
Smooth out the top of each cup, place one "watermelon" slice onto the top of each quiche;
Bake for 35 - 40 minutes, check halfway, if the tops of the quiches are browning too quickly then tent the entire pan with aluminum foil for the remaining baking time;
Garnish the "watermelon" tops with sesame seeds, serve hot or cold, PS, they're just as delicious or even better the next day after refrigerating overnight!