Preheat oven to 375°F (190°C).
Sauce: Into a large (9x13 inch or similar) casserole dish, dump 2 13-oz cans coconut milk, 1 cup vegetable broth, 2 Tbsp Thai red curry paste, 2 Tbsp soy sauce, and 1 Tbsp chili garlic sauce, and 1 Tbsp grated ginger. Whisk to combine.
Fillings: Add 8 oz udon noodles, using a spoon to separate the noodles from each other (they'll stick together if they're touching too much while cooking). Add 1 14-oz package extra firm tofu (cubed), 1 red bell pepper (chopped), 1 cup shelled edamame, and 1 8-oz can water chestnuts (drained). Gently stir to combine.
Bake: Tightly cover with aluminum foil and bake for 20 to 30 minutes, or until noodles are al dente (mostly tender but still have a little firmness in the middle).
Spinach: Stir in 2 handfuls roughly chopped fresh spinach and return to the oven for 10 minutes, uncovered, until noodles are tender.
Serve warm, finishing with fresh lime juice and chopped green onions.
