Prep the lettuce, herbs, cucumbers, and grapes. Place all but the grapes in a large bowl.
Put the salt, mustard, balsamic vinegar, olive oil, and honey in a Mason jar, screw on the lid, and shake until well blended. Taste and adjust, if needed.
Pour half the dressing on the salad and toss. Taste, and if needed, add more dressing. Top with the grapes, feta, and croutons.