In a large frying pan, heat a drizzle of oil over medium-high heat. Add the extra-lean ground beef and cook until browned, about 6-8 minutes, stirring occasionally. When nearly cooked through, add the diced yellow onion, minced garlic, salt, and pepper. Sauté until onions are translucent, about 3-4 more minutes. Stir in one jar of tomato sauce, combining everything well.

Spray the crockpot generously with cooking spray. Start by layering a small amount of the meat sauce at the bottom of the slow cooker, then place uncooked lasagna noodles on top, breaking them to fit as needed. Spread a layer of ricotta cheese followed by a sprinkle of mozzarella. Repeat layering until the slow cooker is full, typically achieving three layers.

After your final layer of noodles, pour the second jar of tomato sauce evenly over the entire lasagna. For added moisture, sprinkle more mozzarella on top and carefully pour some water around the edges of the crockpot.

Cover the slow cooker and set it to cook on high for 3 hours or low for 6 hours. Check for doneness by ensuring the noodles are tender and the cheese is melted and bubbly. Garnish with fresh basil or parsley before serving.