Slice chicken breasts in half horizontally. Place the chicken, cayenne pepper, garlic and 1 tablespoon of oil in a bowl and set aside.
Heat a grill or grill pan over high heat. Toss the corn, zucchini and chiles with the remaining oil. Char-grill or grill the corn and the chilies for about 8 minutes, turning, until tender and blackened in parts. Remove from the heat and chop the chile and place in a bowl. Remove the kernels from the corn cob and place in the bowl with the chile. Grill the zucchini for about 2 minutes per side. Add to the corn mixture, along with the couscous and cilantro and toss to combine. Grill the chicken for about 3-4 minutes per side, or until cooked through.
Serve the chicken sliced over the couscous salad with a lemon wedge for serving.