Preheat the oven to 500°F. Line a baking sheet with parchment paper. In a small bowl, combine the flaxseed meal and water and let sit for 5 minutes. In a large bowl, combine the cooked lentils, garlic, almond flour, salt, and pepper, mixing with a fork or your hands just until combined and the lentils are mashed. Stir in the flaxseed meal mixture (flax eggs). Scoop 1 tablespoon of the lentil mixture and roll it into a ball in your hands then arrange them in a single layer in the prepared baking sheet. Bake the meatballs for 15 minutes.
While the meatballs bake, make the sauce. Whisk together the pineapple juice, ketchup, coconut sugar, soy sauce and tapioca starch mixture. Bring the mixture to a boil and cook until the sauce is thick enough to coat the back of a spoon, 3-5 minutes. Add the pineapple chunks to the sauce. Transfer the cooked meatballs to the skillet with the sauce, spooning sauce over the meatballs. Serve immediately over rice.