Preheat oven to 350°F. Heat oil in large skillet on medium heat. Add shallot and garlic; cook and stir 1 minute or until fragrant. Add bell pepper and tomatillos; cook and stir 3 minutes or until bell pepper is tender-crisp. Add spinach; cook and stir 30 seconds. Add 1 cup of the Monterey Jack cheese, cream cheese, yogurt, jalapeño pepper and sea salt; mix well.
Spoon into 2-quart baking dish. Sprinkle with Cheddar cheese and remaining 1/2 cup Monterey Jack cheese.
Bake 15 minutes or until heated through and edges are bubbly. Serve with vegetable dippers and tortilla chips.