If you haven’t already, take the puff pastry out of the freezer and thaw it out per directions on the box.
Preheat the oven to 425 F.
Heat up the oil in a small saute pan over medium heat.
Add the diced onions and saute until they are just starting to brown on the edges.
Meanwhile, mix 1 cup of shredded cheese, the mayonnaise, and spices together in a mixing bowl. Set aside
Slice the tomatoes about ¼″ thick. I like to use the very top of the tomato, cutting out the part where it was attached to the vine for no waste.
Lay the puff pastry on a cookie sheet.
Spread the onions over the puff, stopping about ¼″ from the outer edges.
Lay the tomatoes over the onions, overlapping them if desired.
Take this opportunity to fold the edges of the puff pastry inwards just a bit, like ⅛″. tomato pie on puff pastry
Spread the cheese and mayo mixture over the tomatoes, using your fingers if necessary to get it to cover the tomatoes as best as possible.
Top the mayo mixture with the remaining ¼ cup of cheese.
Let it bake in the oven for 30 minutes, or until the cheese on top is brown and the puff pastry is puffed and golden brown.