If using a charcoal grill, evenly spread the briquettes. If using gas, set grill to medium hot. Place a 15 inch paella pan in the center of the grill and drizzle with olive oil. Once hot, add the sautéed vegetables, the chorizo, and the rice; mix together until the rice begins to turn transparent, about 3-5 minutes. Add the chicken stock and gently stir until all the ingredients are well combined, being careful that no ingredients are stuck to the bottom. Add the chicken, pressing the pieces deep into the rice mixture, and positioning evenly across the top. At this point, do not stir again.