Heat half the olive oil in a skillet. Add the onion and mushrooms and cook until soft, translucent, and lightly browned.
Pulse half the lentils with the cooked mushrooms and onion in a food processor until combined but still textured.
Combine the processed mixture with the remaining lentils, rice, oats, breadcrumbs, herbs, barbecue sauce, Worcestershire sauce, liquid smoke, salt, garlic powder, basil, and pepper. Rest for 10 minutes.
Shape the mixture into about 18 small meatballs using damp hands or a cookie scoop.
Heat the remaining oil and brown the meatballs in batches, turning gently to develop a crust.
Add barbecue sauce, reduce the heat, and simmer for 1 to 2 minutes until the meatballs are glossy and coated.