Slice cauliflower into ½" steaks. You will get about 2 steaks per head of cauliflower. Put on a baking sheet or in a pan. Drizzle olive oil on top. Sprinkle oregano, salt, and pepper on top. Bake at 450° for 20 minutes, or until starting to brown and become tender.
Sandwiches: Mix basil and vegan mayo. Toast bread.
Spread a tablespoon of basil mayo on four slices of toast. Place a cauliflower steak on each slice. Top with two tablespoons of red pepper tapenade on cauliflower steak. Layer toast on top of tapenade.