I wanted to make something with more flavor and texture than a traditional chicken Caesar salad, something that was worthy of being served to guests. Here it's all about the dressing and seasoning. The variety of ingredients with Mexican flavors creates a savory upgrade from that typical caesar salad.
Marinade/Dressing: Heat the oil in a small skillet over medium heat. Add the garlic and chile, and cook until the garlic is soft and lightly browned, 2–3 minutes. Cool, reserving the oil.
In a blender, add the lime juice, cilantro, 1 teaspoon salt, ½ teaspoon black pepper, and the garlic and chile oil. Purée until smooth. Lay the chicken breasts into a large baking dish; pour a third of the marinade on top, then use tongs to evenly coat the thicken. Marinate in the refrigerator for up to 1 hour.
Heat a grill pan or gas grill to medium to medium-high heat. (Alternatively, start a charcoal fire and let it burn until the coals are medium-hot and covered with white ash.) Lightly brush the onion slices with oil and season with salt. Grill the onion slices and the chicken until the chicken is cooked through and the onion is well-browned, 5–6 minutes per side.
Guacamole: Chop the grilled onion into small pieces and set aside in a bowl. Pit and peel the avocados; add the flesh to the onion. Add half the remaining Marinade/Dressing; then coarsely mash everything together with a potato masher, large fork, or the back of a spoon. Taste and season with salt, about ½ teaspoon.
Salad: Put sliced romaine into a large bowl. Add about half the remaining Marinade/Dressing, and toss to combine.
Assembly: Divide the dressed romaine among four plates. Dollop a portion of the guacamole into the center of each plate. Cut the grilled chicken into cubes and arrange over the guacamole. Sprinkle with cheese and drizzle with remaining Marinade/Dressing before serving.