Over the whole tortilla, spread the black beans. Top with the bison, black beans, and cheese.
Top with the tostada or chips. See picture below to make for placement.
Top tostada with tomatoes, salsa, and spinach.
Place the 1/4th tortilla over the spinach. Carefully pull up each side and secure it by pressing the refried bean edges into the 1/4th tortilla piece.
Spray both sides with a little avocado oil. Cook in a hot pan on each side until golden brown.