Preheat the air fryer: Set to 375°F (190°C). Lightly spray the basket with oil to prevent sticking.

Prep the lentils: If using canned, drain and rinse well. If cooking from dry, simmer 1/2 cup dried lentils in salted water until tender but not mushy, then drain and cool. You’ll need 1 cup cooked.

Make a quick panade: In a large bowl, stir breadcrumbs and milk together. Let it sit for 2 minutes to soften. This helps keep the meatballs tender.

Mix the base: Add grated onion, garlic, parsley, Parmesan (if using), salt, pepper, Italian seasoning, and paprika to the bowl. Stir to combine.

Add protein: Add ground beef and the cooked lentils. Crack in the egg.

Combine gently: Use your hands or a fork to mix just until everything is evenly distributed. Do not overmix or the meatballs can get tough.

Form meatballs: Scoop about 2 tablespoons per meatball (roughly golf-ball sized). Roll lightly with damp hands. You should get 18–20 meatballs.

Load the basket: Arrange meatballs in a single layer in the air fryer basket, leaving a little space between them. Lightly mist the tops with oil for even browning.

Air fry: Cook for 9–12 minutes, shaking the basket or flipping halfway through. Target internal temp is 160°F (71°C). The outside should be browned with some crisp spots.

Batch as needed: If you have more meatballs than the basket can hold, cook in two or three batches.

Serve: Toss with warm marinara, spoon over pasta, or tuck into toasted rolls with mozzarella. A squeeze of lemon and fresh parsley also brighten the flavor.