In a medium bowl, toss the chicken with 1 tsp salt and 1/2 tsp black pepper; set aside. In a large Dutch oven over medium-high, heat the oil until shimmering. Add the onion, fennel and 1/2 tsp salt, then cook, stirring occasionally, until the vegetables begin to brown, about 10 minutes.
Add the tomato paste, garlic, pepper flakes, and orange zest. Cook, stirring often, until the tomato paste begins to darken and stick to the pot, about 4 minutes. Reduce to medium and add the wine. Bring to a simmer and cook, scraping up any browned bits, until the liquid is almost evaporated, about 3 minutes.
Add the chicken, 1.5 cups of water and the saffron, then stir to combine. Bring to a simmer, then reduce to medium-low and cook, uncovered, until a skewer inserted into the chicken meets no resistance, about 15-20 minutes.
Off heat, remove and discard the zest strips. Stir in the orange juice and half the basil, then taste and season with salt and black pepper. Transfer to a serving dish and garnish with remaining basil.