Saute onion in skillet over medium heat in oil until softened, about 4 minutes. Stir in tomatoes and chiles, let cook 2 minutes.
Transfer the mixture to a large bowl and stir in spinach, cheese, cream cheese, half and half, and vinegar. Season with salt and pepper to taste. Spoon mixture into shallow baking dish like a 9 inch quiche dish or pie plate.
Bake in the preheated oven until the dip is bubbly and the top is light brown, about 35 minutes.
