Drain and rinse the chickpeas, then pat them completely dry with a paper towel.
In a large mixing bowl, combine the chickpeas and firm tofu, mashing them together with a fork until a textured, chunky paste forms.
Finely chop the fresh spinach and add it to the bowl along with the crumbled feta cheese, egg, oat flour, cumin, garlic powder, sea salt, and black pepper.
Mix all ingredients thoroughly until the mixture is cohesive, then divide and shape into four even patties.
Heat the olive oil in a non-stick skillet over medium heat.
Place the patties in the skillet and cook for 4-5 minutes per side until they are golden brown and firm.
While the patties are cooking, whisk together the Greek yogurt and lemon juice in a small bowl to create the dipping sauce.
Serve the warm patties immediately with the yogurt sauce on the side.