1. Make the vinaigrette:In a saucepan over medium heat, warm 2 tablespoons of the oil in a saucepan. Add shallot and brown for 2 minutes on each side. Remove from heat and stir in vinegar. Cover, place over low heat, and cook until shallot is tender, about 3 minutes. Transfer mixture to a blender. Add mustard, lemon juice, honey, thyme, and salt. Process on low speed until smooth, about 2 minutes. Remove center of blender lid. With blender on low speed, slowly add remaining oil through center of lid and process until emulsified. Stir in parsley. Refrigerate at least 30 minutes before serving.
2. Make the salad:Cut large tomatoes into ¼-inch-thick slices. (Reserve ends for another use, such as making tomato sauce.) Cut small tomatoes into quarters. Arrange two to four tomato slices on each of four plates. Drizzle with 2 tablespoons of the vinaigrette. Press the lavender flowers with the edge of a knife until they split. Sprinkle tomato slices with lavender. Top each salad with four to six tomato wedges. Drizzle with remaining vinaigrette. Sprinkle evenly with more lavender. Top salads with pea tendrils, salt, and pepper.