Bring a large pot of water to a boil. Dip the chard leaves in the boiling water and quickly remove carefully with a slotted spoon. Place them flat on a paper towel.
Add carrots to the boiling water and cook for 25 minutes, or until tender. Drain and cool.
Lightly oil an 8 x 2 3/4 x 3 1/2 inch terrine or loaf pan. Line with a layer of plastic wrap, leaving enough hanging over the sides to cover the top. Then line the pan with the chard leaves, making sure there are no gaps and leaving enough hanging over the sides to cover the top.
Trim the asparagus at the thicker end so they fit the length of the pan.
Slice each zucchini in half lengthwise, and then each half into four lengthwise.
Steam the asparagus, zucchini and green beans for 6 minutes, or until tender. Drain and refresh in cold water so they keep their color. Pat dry with paper towels.
Puree carrots with 1 cup creme fraiche in a food processor. Season with salt and pepper.
Put 2 tablespoons water in a small bowl and sprinkle with gelatin. Let sit 5 minutes, then put bowl over a pan of simmering water until melted. Add to the carrot puree and mix well.
Spoon a quarter of the carrot puree into the terrine and smooth out. Arrange 6 asparagus spears on top, all pointing in the same direction. Arrange all of the zucchini on top in a flat layer. Add another quarter of the puree and smooth out. Add tomato halves, cut side up. Add another quarter of the puree and smooth. Arrange the remaining asparagus spears, all one direction, and top with green beans (beans can be layered widthwise so they cover layer completely. Top with remaining puree and smooth out. Fold the overhanging chard leaves and plastic wrap over top. Refrigerate overnight.
Fold back plastic wrap from top and unmold onto a plate and peel off plastic wrap.
To make sauce: Fold the herbs and lemon zest into the creme fraiche and season with salt and pepper.
Cut the terrine into 1-inch slices and serve with a dollop of the herb sauce on the side.