Peel and quarter avocados, reserving pits. Coarsely mash avocado with a fork in a nonmetallic bowl. Set aside any that might be too hard to mash easily. Pour grapefruit and lime juice into blender. Add shallot and 2 sprigs each of parsley and cilantro. Blend on high until liquefied. Add blended mixture to mashed avocado, mix gently. Add remaining vegetables,basil and thyme. Stir well. Garnish with reserved cilantro and parsley. If not serving immediately, place in a small bowl with avocado pits,cover and refrigerate. The avocado pits keep the mixture from turning brown.