Bring a pot of salted water to a boil. Add carrots and cook until just tender, roughly 3 minutes. Remove from heat and drain immediately.
In a large bowl, whisk together olive oil, vinegar, garlic, lemon juice, red onion, parsley, mustard, sugar, salt and pepper. Add carrots and toss to coat. Refrigerate and let marinate for at least 4 hours or as long as 2 days.
Recipe by Port and Fin at https://portandfin.com/garlicky-marinated-carrots/