Tender lentil meatballs are baked or air-fried, then cloaked in a sweet-savory French onion gravy—comforting, umami-rich, and perfect over creamy mashed potatoes.
If baking, preheat oven to 375°F. If air-frying, prepare the air fryer basket with nonstick spray.
Make the flax egg: whisk flax meal and water together and let sit 3–5 minutes until thickened.
In a large bowl, mash the cooked lentils. Add the flax egg, bread crumbs, olive oil (for meatballs), liquid smoke, soy sauce, garlic powder, onion powder, and a pinch of salt and pepper. Mix until fully combined.
Roll the mixture into meatballs.
Bake option: Place meatballs on a sheet pan sprayed with nonstick spray. Bake 10 minutes, flip, then bake about 10 more minutes until firm and lightly browned.
Air-fryer option: Spray basket with nonstick spray. Air-fry 8–10 minutes, flipping halfway, until firm and browned.
While meatballs cook, make the gravy: Heat olive oil (for gravy) over medium-high in a large nonstick skillet. Add diced onion and chopped garlic, reduce heat to medium, and sauté 5–7 minutes until starting to brown.
Add thyme sprigs and brown sugar; cook 5–7 minutes more until onions are golden brown.
Stir in flour to coat the onions. Gradually pour in vegetable broth with a pinch of salt and pepper, whisking to combine.
Bring to a simmer and cook about 5 minutes, whisking frequently, until the gravy thickens.
Remove thyme sprigs; taste and adjust seasoning with more salt and pepper. Optionally add a splash of balsamic vinegar if the gravy needs acidity.
Add cooked meatballs to the skillet and toss to coat in the gravy.
Serve immediately, ideally over mashed potatoes if desired.