Position a rack in the center of the oven and heat the oven to 475° F. Line a heavy-duty rimmed baking sheet with parchment. If carrots are thick, cut in half crosswise to separate the thick end from the thin end; halve the thick end lengthwise. Cut all the carrot segments crosswise into 1-inch lengths. In a medium bowl, toss the carrots with enough of the olive oil to coat generously, the salt, and a few grinds of pepper. If using a flavoring before roasting, toss it with the carrots now.
Turn the carrots out onto the baking sheet and arrange the pieces so that they are evenly spaced and lying on a cut side. If the pieces cover the baking sheet sparsely, arrange them toward the edges of the baking sheet for the best browning. Roast the carrots until lightly browned on bottom, 12 to 15 minutes. Flip and continue to roast until the carrots are tender and slightly shriveled, 3 to 5 minutes.
Return the carrots to the bowl in which you tossed them with the oil, or put them in a clean serving bowl. If they seem a bit dry, drizzle them with a little oil. Season to taste with salt, pepper, and lemon juice, if using.