Heat a skillet over medium-high heat. Add ground sausage and cook, breaking it up into small pieces, until browned, about 7 minutes. Transfer to a bowl. Drain and discard grease; wipe out the skillet with a paper towel.

Add butter to the skillet and melt over medium heat. Add onion and sauté until translucent, 2 to 3 minutes. Add garlic and cook until fragrant, about 1 minute. Whisk in flour until evenly mixed with melted butter, about 1 minute. Slowly pour in chicken broth and cream; whisk until mixture comes to a boil, then immediately reduce the heat to low. Simmer until mixture thickens, whisking occasionally, about 10 minutes.

Return sausage to the skillet; add gnocchi, spinach, and tomatoes. Increase the heat to medium and cook until gnocchi is heated through, 2 to 3 minutes. Season with salt and pepper. Garnish with Parmesan cheese.