Whisk together the paprika, cumin, mustard, fennel, pepper and salt in a small bowl.
Brush the chicken with a few teaspoons of oil on both sides. Rub the breasts on the skin side with some of the rub and place on the grill, rub side down. Grill until golden brown and slightly charred, 4 to 5 minutes. Turn the breasts over and continue cooking until just cooked through, 4 to 5 minutes. Transfer the chicken to a platter and immediately drizzle with some of the Parsley-Mint Sauce. Let rest 5 minutes. Serve with additional sauce on the side.
Place the mint, parsley, garlic and serranos in a food processor and process until coarsely chopped. Add the honey and mustard and process until combined. With the motor running, slowly add the olive oil until emulsified.
Transfer the mixture to a bowl and whisk in a few tablespoons of cold water to thin to a sauce-like consistency. Season with salt and pepper to taste.