Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Finely mince the portobello mushrooms, celery stalks, and garlic cloves into very small, uniform pieces.
Heat a non-stick skillet over medium heat and sauté the minced mushrooms, celery, and garlic with a tablespoon of water until they are softened and fragrant.
In a large mixing bowl, whisk the eggs until they are well combined and slightly frothy.
Add the cooled sautéed vegetable mixture and the ground beef to the bowl with the eggs.
Season the mixture with the sea salt, black pepper, cumin powder, and paprika.
Gently mix the ingredients together with your hands until just combined, taking care not to overwork the meat to keep the texture light.
Roll the mixture into 1.5-inch balls and arrange them evenly on the prepared baking sheet.
Bake for 15 to 18 minutes or until the meatballs are browned on the outside and fully cooked through.