Preheat the oven to 450 degrees F (230 degrees C). Place falafel on a baking sheet. Bake in the preheated oven until heated through, 8 to 10 minutes. While falafel bake, whisk tahini, water, lemon juice, garlic, and paprika together in a bowl. Cut about 1 inch from the top of each pita to form a pocket. Add 2 falafel to each pita with equal amounts lettuce, tomato, cucumber, pickle, and red onion. Drizzle each with about 1 tablespoon tahini sauce and some harissa.