Preheat oven to 400 degrees.

In a large deep skillet, heat the olive oil over medium-high heat.

Add the onions to the pan and cook until softened, approximately 3-5 minutes.

Stir in the carrots and celery. Cook until softened, about 4 minutes.

Add the garlic and cook for one more minute.

Sprinkle the cornstarch over the vegetables and toss to coat thoroughly.

Slowly stir in the chicken stock and bring the mixture to a boil while stirring constantly.

Turn the heat to low and stir in the half and half, mustard, thyme, salt, pepper, peas, noodles and tuna.

Allow the casserole to simmer, uncovered, for 5-6 minutes until the noodles begin to soften.

Stir in the cheese.

In a small bowl, toss the butter with the panko and then sprinkle the mixture over the casserole.

Transfer the skillet to the oven and bake for 15-20 minutes or until golden and bubbling.

Serve immediately.