Bring salted water to a boil in a large pot.
Thinly slice the bottom of 1 spring onion, then mince. Place the minced onions in a bowl with the juice of 1 lemon and sprinkle with salt.
Cut the stems off 1 head of Romanesco. Using a paring knife, start at the base and cut the florets off the central core. Cut the largest florets in half.
Parboil the florets until they are just tender, then drain the pot and rinse them to cool slightly, then toss with the lemon juice and onion and let sit for 5 minutes.
Whisk 1 T. tahini, 3 T. whole milk yogurt, and 1 T. olive oil together. Add a dash each of cumin and paprika. Season with salt and pepper. Toss half the mixture with the romanesco.
Add 2-3 T. lemon juice to the remainder of the dressing.
Separate the leaves of 1 head of lettuce, then wash and spin dry.
Wash 2 carrots and julienne or grate them.
Toss the lettuce and carrots with the remainder of the dressing, then serve the romanesco on a bed of salad.