Set a skillet on medium high heat. Add the plant-based butter or olive oil.
Place the chopped onions in the skillet and sauté until golden.
Add the rice, mint, parsley, salt and pepper.
Dilute the bouillon (cube or paste) in the hot water. Add to the rice mixture. Simmer until the water evaporates, stirring constantly with a wooden spoon.
Remove from heat.
Add the soy or chickpea flour, bread crumbs, and lemon juice. Stir to combine.
Preheat oven to 350°F
Wash the zucchini, trim ends, and cut in half. Scoop out each center leaving about 1/4 inch of the rind to make a zucchini boat.
Fill the zucchini boats with the rice mixture and place in a baking pan.
Cover with parchment paper and then foil.
Bake for 45 minutes to 1 hour or until zucchini is tender-crisp.
Serve with the Avgolemono Sauce. Sprinkle with cayenne pepper or hot pepper flakes, if desired.