Paleo Poached Whitefish in Tomato-Fennel Broth

1 tablespoon olive oil

2 bulbs fennel, chopped

1 onion, chopped

1 ½ pounds whitefish fillets

1 pinch saffron

1 tablespoon fennel seeds

1 cup diced tomatoes

1 cup water, or more as needed

Heat olive oil in a skillet over medium heat. Stir in fennel bulbs and onion; cook and stir until the onion has softened and turned translucent, about 5 minutes. Add whitefish, saffron, fennel seeds, tomatoes, and water. Bring to a boil, cover, and remove from heat. Let sit covered until fish flakes easily with a fork, about 10 minutes.