Preheat the oven to 375°F (190°C).

In a large pot, bring salted water to a boil and cook your pasta until al dente, about 8-10 minutes. Reserve ½ cup pasta water, drain and set aside.

In a skillet, heat olive oil over medium heat, add chopped onions, and sauté for about 4 minutes until translucent. Stir in minced garlic and cook for an additional minute.

In a mixing bowl, combine sautéed onion and garlic with Greek yogurt, Dijon mustard, and half of the cheese. Mix until smooth.

Gently fold in drained tuna, cooked pasta, and frozen peas until well combined, then transfer to a greased baking dish.

Sprinkle the remaining cheese on top. Optional: Mix breadcrumbs with olive oil and sprinkle over the cheese.

Bake uncovered in the preheated oven for 20-25 minutes until cheese is bubbly and the top is golden.

Let it rest for about 5 minutes before serving.