If you’re using a barbecue, make sure it’s lit an hour ahead so the coals are glowing white when you start cooking.
Roughly chop the rosemary and thyme leaves. Pop them in a dish with 2 tsp olive oil. Peel and grate or crush the garlic. Stir into the herbs with some salt and pepper.
Add the lamb chops to the herbs. Turn a few times to coat in the herbs and garlic. Leave them to marinate for 10-15 mins. If the sun's not shining, you can grill the lamb chops instead of barbecuing them. Set your oven's grill to a high heat to warm up.
Halve or quarter any spuds that are particularly large. Pop them in a pan. Pour over enough boiling water to cover them. Bring to the boil. Simmer for 10-15 mins till the potatoes are easily pierced with a fork.
Trim and finely slice the spring onions. Submerge the radishes with their leaves in water. Give them a good swirl, then drain and pat dry with kitchen paper. Slice the leaves off the radishes. Shred the leaves. Halve or quarter the radishes. Finely grate the zest from the lemon, then juice it.
When the potatoes are tender, drain them. Tip them back into the pan. Add the spring onions and radishes with the lemon zest and lemon juice. Season. Toss to mix.
Pop the lamb chops on the barbecue and cook them for 15-20 mins, turning every so often, till they’re charred and cooked through to your liking. If you're cooking indoors, line your grill pan with foil and grill the chops on a rack for 10-15 mins till they’re cooked through.
Add the radish leaves to the potatoes. Toss and serve the potato salad with the lamb.