Rich and creamy, these individual mousses make an interesting first course.
Make sure your avocados have a good flavor but aren't overripe with a lot of brown spots. When you scrape out the avocado, use a spoon to get at the dark green flesh closest to the skin; the mousse is meant to be a nice green color, so discard any discolored areas. The texture of the mousse can be smooth or chunky; the choice is yours. If you want it silky smooth, purée the avocados and scallions in a blender or food processor, then proceed with the recipe.
Lightly brush 8 wells of a nonstick muffin pan with canola oil. Set aside.
Place the water in a small saucepan and sprinkle with the gelatin. Let the gelatin soften for 1 minute. Heat the mixture over low heat, stirring to dissolve the gelatin, about 2 minutes. Remove from the heat and set aside while you proceed with the recipe.
Mash the avocados in a small bowl with a fork or potato masher. Add the gelatin mixture and the remaining ingredients, stirring to thoroughly combine.
Spoon the mousse into the prepared pan. Rap the muffin pan firmly on the counter once or twice to settle the mousse and release any air bubbles. Cover with plastic wrap and refrigerate until the mousse is set, at least 4 hours or overnight.
At serving time, run a small knife around the perimeter of each mousse to loosen it from the pan. Set a lettuce leaf on each of 8 small plates. Remove the mousses from the pan and invert, arranging one on top of each lettuce leaf. Garnish each serving with a tomato rose and a sprig of fresh parsley, if using, and serve with toasted croutes or crackers.