Preheat the oven to 375 degrees. In a large bowl, combine the ground beef, breadcrumbs, egg, Italian seasoning, onion, minced garlic, salt, and pepper. Mix until just combined.
Line a loaf pan with parchment. Press half the meat mixture into the bottom. Spread the ricotta cheese evenly over the meat layer, then top with the remaining meat mixture. Press gently to seal the edges.
Bake the meatloaf for 45 minutes. Remove from the oven, sprinkle the shredded mozzarella over the top, and return to the oven for 10 more minutes until the cheese melts and the internal temperature reaches 160 degrees.
While the meatloaf rests, heat the olive oil in a large skillet over medium heat. Add the sliced garlic and cook for 1 minute until fragrant. Add the broccoli rabe, salt, and pepper. Cook for 5 to 7 minutes, stirring often, until the greens are tender.
Slice the meatloaf and serve portions with the garlic broccoli rabe on the side.