Start by mixing together the Greek yogurt, chopped basil, minced garlic, and sriracha sauce in a bowl to prepare the spread.

Slice the tomatoes and avocados into even pieces for layering in the sandwich.

Take two slices of whole wheat bread, spread a generous amount of the garlic-basil mixture on one side, layer with tomato and avocado slices, season with salt and pepper, and top with another slice of bread.

Cut the sandwiches in half if desired and serve immediately.