Preheat your oven to 220°C/200°C fan/gas mark 7.
Halve, peel and thinly slice the shallot. Peel and grate the garlic (or use a garlic press).
Halve the pepper and discard the core and seeds. Slice into thin strips. Trim the courgette, then quarter lengthways. Chop widthways into small pieces.
Drain and rinse the mixed beans in a sieve.

Heat a drizzle of oil in a large frying pan on medium heat.
Once hot, add the shallot, pepper and courgette. Stir-fry until softened, 5-6 mins, then add the garlic and Mexican style spice mix (add less if you don't like too much heat). Cook for 1 min more.
Stir in the mixed beans, chopped tomatoes and vegetable stock paste, then simmer until the liquid has reduced by half, 10-12 mins. Add a splash of water if gets too thick.

While the beans and veg simmer, roughly chop the coriander. Grate the Cheddar cheese. Halve the lime.

Lay the tortillas (2 per person) onto a large baking tray in a single layer and rub each with a little oil.
Season with salt, then bake on the top shelf of the oven until golden and crispy, 4-6 mins.<.p>

Meanwhile, halve the avocado and remove the stone. Use a tablespoon to scoop the flesh into a bowl.
Add half the coriander and a squeeze of lime juice to the avocado and mash together with a fork. Season with salt and pepper, then set your guacamole aside.

When everything is ready, taste and season the beans with salt and pepper if needed.
Pop the tostadas on your plates and top with the bean mixture and guacamole - as much as you'd like.
Sprinkle over the cheese and remaining coriander to finish. TIP: Tostadas are best enjoyed eaten by hand - get stuck in! Enjoy!