Preheat the oven to 400F/200C.
Peel the carrots and cut into lengths, then divide each length depending on thickness - around 4 pieces for thicker end and 2 for thinner end, but may be less with thinner carrots. Trim the base off the fennel and cut off the majority of the stems. Divide the bulb top to bottom and cut out the majority of the core, but leave enough so it holds together.
Trim the base off the fennel and cut off the majority of the stems. Save some of the fronds and chop to use later. Divide the bulb top to bottom and cut out the majority of the core, but leave enough so it holds together. Cut into slices, roughly the same thickness on the wide side as the carrots, cutting through the core so the layers hold together, as far as possible.
Place the chopped vegetables on a baking sheet and drizzle over olive oil, salt and pepper. Toss gently, particularly the fennel, so they are coated on all sides relatively evenly. Roast for approximately 25 - 35 minutes, depending on your own and the size of the vegetables, until they are tender and just starting to brown around the edges.
Whisk together the oil, lemon juice, honey, salt and pepper for the vinaigrette, if using (it will work without but it adds a nice brightness). Alternatively, you can shake in a small jar. Be sure to give a little stir to make sure the honey is dissolved. You may need to re-shake/whisk right before using.
Transfer the roasted vegetables to a serving plate, or serve up on individual plates, and top with a little reserved fennel fronds and the vinaigrette, if using. Works both arm and at room temperature.