To make the chorizo sauce take the sausages out of their casings and fry them up in a saucepan while breaking them up with a wooden spoon. When the sausages are nearly done, add the chopped onions and sauté for 5-7 minutes until tender, then add the pressed garlic cloves and let them cook for about 30 seconds.
Pour in the tomato passata or crushed tomatoes and stir to combine, then add smoked paprika and chilli flakes, bring to a boil and let the sauce simmer for 5 minutes. Add salt to taste at the end. The sauce shouldn’t be runny. It should hold its shape when scooped with a spoon.
While the sauce is simmering, make the lime crema by coming the sour cream with freshly squeezed lime juice.
Preheat the oven to 200C/400F. Line a shallow baking tray or a sheet pan with parchment paper, then scatter the corn tortilla chips in an even layer. Use half of the amount of the chorizo sauce and dab all over the chips. Reserve the second half of the sauce for another use or freeze for later.
Top the chips with the grated cheddar cheese all over, and scatter the sliced green chilli, bake in the preheated oven for 5-7 minutes, until the cheese is melted. The cheese should be oozy by the end of the cooking time, not hard.
Remove from the oven and top with pico de gallo, sliced green onions and a drizzle of the lime crema. Alternatively you can serve the topping on the side to avoid the nachos going soggy.