Heat olive oil in a large skillet or Dutch oven over medium-high heat. When the oil shimmers, add the sausage and garlic (if you prefer softer vegetables, you can add the bell pepper and onion at this point, too). Cook and stir until the fully-cooked sausage is browned (about 5 minutes), or until the fresh sausage is cooked through (about 7-9 minutes).
Add the bell pepper, onion, broccoli, tortellini, marinara sauce, and broth (or water). Bring to a boil.
Once the mixture boils, turn the heat to LOW, cover, and simmer for about 7-9 minutes (or until the tortellini is tender). Remove from the heat.
Remove lid, sprinkle mozzarella over the tortellini, and place the lid back on top until the cheese melts (about 1 minute). Taste and season with salt and pepper, if desired. Garnish with Parmesan and fresh herbs.