In a medium bowl, combine the lemon juice, thyme, mint, garlic, lemon zest and sugar. Whisk in 1/3 cup of the oil and season with salt and pepper.
In another bowl, toss the mesclun and tomatoes with 1 tablespoon of the dressing. Mound the salad on plates.
Heat the remaining 1 tablespoon of oil in a large skillet. Add the corn, edamame and bell pepper and cook over moderately high heat until crisp-tender, about 3 minutes. Add to the dressing in the bowl, season with salt and pepper and toss. Spoon the succotash over the salad and serve.