The G2 weekly recipe: Tuna ceviche tacos

This is in my top five summer lunches ever. When it comes to ceviche dishes, you simply have to hand it to the Mexicans, who are spoilt for sea - providing great fish as well as salt - and sun, which also ripens the limes, a vital ingredient. This is just the simplest, most moreish, healthy lunch in the world. No cooking required - it is the lime juice that technically cooks the fish. Forget the BBQ, this is the way to eat when the sun shines.

Serves four, or more as a snack

500g of fresh, fresh, fresh tuna cut into 1cm dice

Big handful coriander, chopped

1 clove of garlic, finely minced

1-2 red chillies, sliced or diced

Juice of 1-2 limes

Handful of mung bean sprouts

Handful of breakfast radishes, sliced

2 spring onions, thinly sliced

A few leaves of cos or baby gem lettuce

Tortillas, about 12 small ones or four big ones. I like corn, but flour, either grilled or deep-fried to crispy, are all good too. It's really just a vehicle.

1-2 ripe avocados

Salt

Mix the tuna with the coriander, garlic, chillies, lime juice, onions and a hefty pinch of sea salt - definitely not the table variety.

From here, this isn't so much a recipe as building directions: lay some lettuce on a tortilla, squish on some avocado, pile on the tuna mix, sprinkle sprouts and radishes, then have a taste. Play with the lime-salt balance and, please, reach for the hot sauce if you're brave enough - you can get an interesting sensation from the heat of the chillies and the coolness of the tuna.

· Allegra McEvedy is co-founder of the fast-food chain Leon. Her award-winning cookbook is published by Kyle Cathie, price £19.99. To order for £18.99 with free UK p&p, call 0870 836 0875 or go to guardian.co.uk/bookshop