Cut carrots in half lengthwise. Heat a large cast-iron skillet over medium-high. Add olive oil and butter to pan; swirl to coat. Add carrots in a single layer; cook without stirring for 5 minutes. Stir, and arrange in a single layer; cook without stirring for 5 more minutes. Combine water, hoisin sauce, maple syrup, and salt; add to pan, and cook 1 minute or until carrots are glazed.