Blend together oils, mustard, vinegar, lime juice, cilantro, oregano and pepper. Combine 1-1/2 cups mustard mixture and chicken. Marinate in refrigerator for at least 2 hours. In blender or food processor, blend avocados with remaining mustard mixture and sugar until smooth. Cover and chill until serving time. Remove chicken from marinade. Grill 6 inches from heat source, over medium-high heat, brushing with marinade often until chicken is done. Keep warm. To serve, arrange about 2 cups salad greens on individual salad plates. Slice 1 chicken breast half and arrange on greens.Top with 2 ounces avocado dressing. Garnish if desired and serve immediately.