Peel the husks and fibres away from the sweetcorn cobs and discard. Slice a sliver from the base of each cob so it can stand upright. Stand a cob in a large shallow bowl and run a sharp knife down the sides to remove the kernels. Repeat with the other cob. Peel and grate or crush the garlic clove.
Place a dry frying pan on the hob for a few mins. When warm, drizzle in 1 tbsp olive oil and add the sweetcorn kernels with a large pinch of salt and 1 tbsp cumin seeds. Toast for 4 mins, tossing the pan regularly till most of the kernels are golden.
Add the garlic and cook for a further 1 min, stirring. Tip the cooked corn into a large bowl to cool.
While the corn is cooling, chop the tomatoes into 2cm-thick cubes. Add to the bowl with the corn.
Halve the avocado and scoop out the flesh with a spoon, discarding the stone. Cut the avocado into chunks of a similar size to the tomato. Add them to the bowl. Zest and juice the lemon over the top and lightly toss together. This will stop the avocado from browning.
Finely chop the parsley stalks and roughly chop the leaves. Tear the basil leaves. Add the herbs to the bowl. Drizzle in ½ tbsp olive oil and add some salt and pepper. Toss together. Taste the salad and add more salt or pepper if you think it needs it, then serve.