Using poultry shears, cut the chicken breasts in half crosswise. Pat dry and sprinkle on both sides with salt and pepper. In a large nonstick frying pan over medium-high heat, warm the oil. Add the chicken and cook until brown, about 3 minutes per side. Transfer to a plate.
Pour off the fat from the pan and return the pan to medium-high heat. Add the pancetta and fennel seeds and sauté 30 for seconds. Add the onion, sliced fennel bulb, and bay leaves. Sauté until the vegetables begin to brown, about 5 minutes. Stir in the tomato paste. Add the wine and bring to a boil, stirring up the browned bits.
Return the chicken to the pan with any juices accumulated on the plate. Add the broth and bring to a boil. Reduce the heat to medium-low, cover, and simmer until the chicken is cooked through, turning after 6 minutes, 12–15 minutes total, depending on the size of the chicken. Taste and adjust the seasoning.
Divide the polenta between 2 warmed plates. Top with the chicken and sauce. Sprinkle with minced fennel fronds and serve right away.