Heat the olive oil in a large saute pan over medium-high heat and add in the onions, mushrooms and asparagus. Cook for 4 to 6 minutes or until lightly browned.
Next, add in the peas and spinach and cook for 2 minutes. Season with salt and pepper and set aside to cool.
In a large bowl whisk together the eggs, cream, 5 ounces of shredded fontina cheese, salt and pepper until combined and then fold in the sautéed vegetables. Set aside.
Roll out the puff pastry sheet on a clean surface dusted with flour and then fit it into a 9” fluted pan. Remove and excess dough and discard.
Dock the bottom of the pan with a fork and pour in the egg and vegetable mixture and evenly add on the tomatoes and remaining 1 ounce of cheese and bake in the oven for 35 to 40 minutes or until lightly browned on top and firm in the center.
Garnish with basil and cool for 15 to 20 minutes before slicing and serving.