Cook the egg noodles in a large pot of salted water for 2 minutes less than the package directions. Drain and set aside.
Melt the dairy free butter in a large oven-safe skillet over medium heat. Add the onion and mushrooms, and cook for 7 to 8 minutes until softened and lightly browned.
Stir in the garlic and flour. Cook for 1 minute, stirring constantly.
Gradually whisk in the chicken broth and dairy free milk. Simmer for 4 to 5 minutes until smooth and thickened.
Stir in the lemon juice, Dijon mustard, salt, pepper, tuna, peas, and cooked noodles.
Combine the dairy free breadcrumbs, olive oil, and dairy free parmesan-style cheese. Sprinkle the mixture evenly over the casserole.
Bake at 375 F for 20 to 25 minutes, until bubbling around the edges and golden on top. Rest for 5 minutes before serving.