Preheat the oven to 180C. Melt the butter or margarin and let it cool.
Grease the holes of a muffin tin.
Put 3 filo sheets on top of each other and cut out approx. 10 x10 cm squares. Put them on a plate and cover with a dump kitchen towel.
Lay a filo square on a chopping board, brush it with the melted butter, then add another square on top, slightly turned. Brush this with butter too then put another square on top, again angled.
Put this shape into one of the tin holes, slightly pushing down with your fingers.
Repeat with the rest of the filo squares. You should get 12 filo cases.
Bake for about 8 minutes or until golden all over. Let them cool in the tin for a couple of minutes, then carefully remove them to a platter. Let them cool.
While the cases are cooling, cut the avocados in half, remove their stone stone, then skin. Cut the flesh into small cubes. Put them in a bowl. Immediately squeeze some lemon juice over them to prevent colouring.
Chop the tomatoes and spring onions, add these to the avocados. Season with salt and pepper.
Drizzle with a drop of olive oil and some tabasco. Add more lime juice.
Combine gently, taste and adjust the seasoning, tabasco and lime juice to your liking.
Fill the tarts with the mixture.
Serve with chopped coriander leaves scattered on top.