Cut the asparagus on the diagonal into 1 1/2-inch pieces. Cut the carrots on the diagonal into 1/4-inch pieces.
Fill a bowl with ice water. Bring a pan of water to the boil. Add the asparagus and time 3 minutes, starting the time as soon as the vegetable goes into the water. With a wire or slotted spoon remove the vegetables to the bowl of ice water and bring a pan of water back to a boil. Add the carrots and peas; time 2 minutes. Drain and plunge the vegetables into the ice water.
When the vegetables have cooled, drain and wrap in paper towels. Put into a plastic bag and refrigerate.
In a blender or small food processor combine the garlic, mustard, lemon juice and vinegar. Slowly add the oil, blending until emulsified. Add the salt, pepper and herbs. (The dressing can also be whisked together by hand.)
When read to serve, combine the asparagus, carrots and peas with the tomatoes. Pour the dressing over the vegetables, stirring until well coated.