I poached the tilapia fillets in the cream sauce with the vegetables, i.e., a sauce of vegetable stock, heavy cream, cabbage, shiitake mushrooms, dijon mustard, fennel seed, thyme, salt and pepper. I used dried mushrooms, but the texure of fresh mushrooms would likely be better with this delicate fish.
I prepared couscous in vegetable stock and served it layered in the middle.
This was inspired by a related recipe for Pan-Seared Cod with Creamy Fennel Ragoût.