Preheat the oven to 425 degrees . Add the gnocchi and cook for 3-4 minutes or until they float to the top of the pot. Add spinach in at the last minute of cooking to wilt. Drain and transfer to the baking dish. Add the tuna and pesto and stir to combine. Add salt and pepper, to taste.
In a medium bowl, toss the breadcrumbs and cheese. Sprinkle the breadcrumb mixture evenly over the gnocchi and bake until heated through and golden, about 15 minutes.
Serve warm with extra pesto or olive oil drizzled on top if desired.