Bring a large pot of salted water to a boil. Cook red lentil pasta according to package instructions until al dente, usually 8-10 minutes. Drain and set aside.
Heat olive oil in a large skillet or Dutch oven over medium heat. Add onions and sauté until translucent, 3-4 minutes. Add garlic and cook 1 minute until fragrant.
Increase heat to medium-high. Add lean ground beef, breaking it apart with a spatula, and cook until browned and no pink remains, about 5-7 minutes. Drain excess fat if needed.
Stir in crushed tomatoes, Italian seasoning, salt, and pepper. Reduce heat to low, cover, and simmer 10-15 minutes until sauce thickens.
Combine cooked pasta and sauce in the pan, gently stir to coat evenly. Serve immediately with optional grated Parmesan cheese (if following lactose-free, omit or substitute).