Boil the tomatillos with the garlic, onion, and pepper. As soon as the tomatillos change color, turn off the heat—if they burst or overcook, they can become bitter.

Blend the tomatillos with the cilantro, onion, pepper, and garlic. Pour the mixture into a pot and heat it up. Season with salt, pepper, and chicken bouillon if using. Adjust the consistency with a little water if needed. Cook your quesadillas on a griddle or skillet until golden brown, then serve them topped with the green salsa, lettuce, sour cream, and onion.