Heat olive oil in a large skillet over medium heat. Add onion and garlic and cook until softened, about 5 minutes.
Stir in dried thyme and Dijon mustard.
Add milk and bring to a simmer.
Add egg noodles and season with salt and pepper. Cook, stirring occasionally, until noodles are cooked through and most of the liquid has been absorbed, about 10 minutes.
Stir in tuna, frozen peas, and grated cheddar cheese until cheese is melted.
Remove from heat and stir in sour cream.
Serve hot topped with crushed Ritz crackers.
