Prepare the tofu. Warp the tofu block in a paper towel and squeeze the excess water. If it has a lot, press it between two surfaces, weighing down the top. You can also use a commercial tofu press.
Cut and season tofu cubes. Cut the tofu into cubes that are ½ - ¾ of an inch. Add the lemon or lime juice and soy sauce to a shallow dish and toss the cubes. Before baking or air frying, toss the tofu cubes with 1 tablespoon of cornstarch until it is absorbed.
To bake the tofu. Preheat the oven to 425 F (220 C). Add the tofu pieces, separated into a single layer, on a baking tray lined with parchment paper or a silicone baking mat. Bake the tofu for 15 minutes, then toss the cubes and bake for another 5-10 minutes until it is brown and crispy.
Air Fry. Preheat the air fryer to 325 F (190 C). Add the tofu cubes, separated, in a single layer. Air fry for 10-12 minutes, shaking it after 5 minutes. You may need to adjust the time depending on the size of the tofu cubes.
Make the curry sauce. Heat a pot over medium heat. Then add the onions and peppers. Sauté the ingredients for 2-3 minutes until they soften. Then the garlic, ginger, and 1 tablespoon of curry powder. Mix and then add the tomatoes and tomato paste. Stir well.
Add coconut milk and tofu. Stir in the coconut milk and baked tofu. Let the sauce simmer for about 5 minutes.
Finish the curry. Fold in the chopped spinach, lime juice, and zest. Cook for another minute to wilt the spinach.
Serve over rice and garnish with chopped cilantro and lime wedges if desired.