Bring a large pot of heavily salted water to a boil. Add the spaghetti and cook, about 10 minutes, until just shy of al dente. Reserve about ½ cup of the pasta water. Drain, toss with 1 tablespoon of the olive oil and set aside.

Preheat the oven to 350°F. Spray a 13x9-inch baking dish with nonstick spray. Set aside.

Heat the remaining tablespoon of olive oil in a large dutch oven over medium-high heat. Add the onion and bell pepper along with a pinch of salt and pepper. Saute for about 5 minutes, until the onion is translucent and soft.

Add the diced tomatoes with chilies and cook until most of the liquid has evaporated, about 5 minutes.

Add the mushroom and chicken soup and chicken stock. Bring to a simmer.

Add the cheeses and stir in until melted and the sauce is creamy. Add the chicken. Taste and season with salt and pepper as desired.

Stir the cooked spaghetti into the sauce. If needed, use some of the reserved pasta water to thin the sauce and bring the mixture together.

Transfer to the prepared baking pan.

Bake for 30-40 minutes, until the sauce is bubbly and the top is golden. Serve hot.