Hold 1 ear of corn upright, stem end down, in the center of a wide, shallow bowl. Using a sharp knife, slice straight down between the kernels and the cob, rotating the ear a quarter turn after each cut. Repeat with the second ear. You will have about 1 cup kernels.
In a large salad bowl, combine the corn, tomato, cucumber and onion.
Combine the basil, mint, parsley, dill and garlic on a cutting board and finely chop. Add to the vegetables.
In a small, dry fry pan over medium-low heat, warm the cumin just until fragrant, about 20 seconds.
Transfer to a small bowl.
Add the olive oil, vinegar, salt and a grind of pepper and whisk until blended.
Carefully rinse the spinach in 2 or 3 changes of water.
Drain briefly in a colander and pat dry with a kitchen towel.
Add the spinach and the dressing to the corn-tomato mixture.
Toss to mix and coat with the dressing.
Serve immediately.