Preheat oven to 350°.
Melt butter in a large nonstick skillet over medium heat. Add onion and garlic; sauté 5 minutes or until tender. Add spinach, water chestnuts, and artichokes; sauté 2 minutes. Add cream cheese, sour cream, 1/2 cup Cheddar cheese, and next 3 ingredients.
Spoon into an 11 x 7-inch baking dish coated with cooking spray. Top with remaining 1/2 cup Cheddar cheese. Bake at 350° for 18 to 20 minutes or until thoroughly heated. Serve with baked tortilla chips.