Preheat the oven to 350°F (175°C).
In a mixing bowl, combine the drained tuna, chopped onion, shredded cheese, frozen vegetables, and eggs; stir until evenly mixed.
Spray a 13x9-inch baking pan with nonstick spray and unroll one package of crescent rolls to form a single sheet covering the bottom of the pan.
Spread the tuna mixture evenly over the first crescent roll sheet.
Unroll the second package of crescent rolls and place it over the filling, pressing the seams together so it appears as a continuous top sheet.
Bake in the preheated oven until the top is golden brown, about 25 minutes.
Remove from the oven and, if desired, sprinkle additional cheese on top; let rest a few minutes before slicing and serving.