Preheat oven to 350F.

In a large skillet, heat olive oil over medium-high heat. Add mild Italian sausage and diced onion. Cook, breaking up the sausage, until the onion is translucent and the sausage is cooked through. Drain and return to pan. Add garlic and cook just until fragrant, about 30 seconds. Add cream cheese, diced tomatoes with green chiles, and chopped spinach. Stir until cream cheese is melted. Remove from heat and stir in about half of the shredded monterey jack.

Transfer mixture to an 8x8-inch pan and sprinkle with remaining cheese.

Bake for about 15 minutes, until bubbly. Serve hot with tortilla chips.