Drain the tofu packages and remove the tofu. Slice the blocks horizontally so they are half their original height. Cut the rectangles diagonally into 2 triangles each. Set them on paper towels to drain while you prepare the marinade.

Halve one grapefruit and one orange and squeeze 1/2 cup of juice from each. Stir in 1 tablespoon of olive oil. Blot the tops of the tofu with more paper towels. Arrange the tofu in a single layer in a large dish. Season with the cayenne pepper and 1/8 teaspoon salt. Mix the marinade well and pour it over the tofu. Cover with plastic wrap and allow to marinate over night or for at least several hours, turning once.

Make the salsa now if you have time. Peel the remaining grapefruit and oranges. Use a paring knife to remove the outer membrane. Work over a bowl to catch the juices, and cut between the membranes to release the segments. Repeat with the oranges. Halve each fruit segment. Add the diced bell pepper, red onion, and cilantro. Season with remaining 1/8 teaspoon of salt. Cover and refrigerate.

When youre ready to cook the tofu, heat a grill pan over high heat and add 1 teaspoon olive oil or use a non stick frying pan. Add the tofu and marinade and cook about 3 minutes on each side, turning gently with tongs or a spatula. Remove the tofu and add the spinach to the pan. Stir it around briefly so it just wilts, about 1 or 2 minutes. Arrange spinach in the center of 4 plates. Lay 2 triangles of tofu on top. Spoon grapefruit salsa around the tofu and garnish with fresh avocado chunks.