Cut lettuce and spinach; slice tomatoes in half; drop into a large bowl for mixing.
Cut cucumbers into slices (removing skin if desired), slice pepper into strips, chop onions. Place these ingredients into bowl along with feta and olives.
Mince garlic, then whisk together with remaining dressing ingredients. (It is also convenient if you have a mason jar with a top to just add these ingredients and shake away!)
Pour dressing over salad just before serving, toss together all ingredients, serve with a small dinner roll and watermelon.