Peel cucumbers in alternating stripes (peel a strip and then leave one unpeeled next to it - repeat until entire cucumber appears striped).
Cut cucumbers in half along the length and scrape out the seeds. Cut halves diagonally into ½-inch-wide pieces.
Place in large bowl an add vinegar, sugar and salt. Let stand at room temperature 1 hour, stirring occasionally.
Add tomatoes, red onion, mint and oil to cucumbers and toss to blend. Season with fresh ground pepper.