Preheat your oven to 220°C. Pop the tortillas in a single layer on a lightly-oiled baking tray and drizzle over a little oil. Season with salt and black pepper. Set aside.

Halve, peel and thinly slice the shallot into half moons. Peel and grate the garlic (or use a garlic press). Halve, then remove the core from the yellow pepper and thinly slice into 1cm wide strips. Remove the top and bottom from the courgette, cut lengthways into strips then chop into roughly 1cm chunks. Drain the mixed beans in a colander and rinse under cold running water.

Heat a drizzle of oil in a frying pan on medium heat. Add the shallot, pepper and courgette, a pinch of salt and a grind of black pepper. Cook until soft and brown, 5-6 mins. Add the garlic and fajita spice (add less spice if you're not a fan of heat!) and stir well. Cook for 1 minute more. Next, add the mixed beans, plum tomatoes and vegetable stock pot. Cook until the liquid has reduced by half, 10-15 mins.

Meanwhile, pop the tortillas on the top shelf of your oven. Warm for 6-10 mins. Keep an eye on them, you want them to be golden and crispy but not burnt! When ready, remove from your oven and lay on some kitchen paper to absorb any excess oil.

Grate the cheddar cheese. Halve the avocado lengthways and twist apart. Remove the stone and slip a spoon around the edge of the flesh to pop the flesh out of its skin. Put the avocado in a mixing bowl and add the coriander stalks and half the coriander leaves. Squeeze in some lime juice and mash together with a fork (it doesn't have to be completely smooth).

Lay one tostada on each plate and pile high with the beans. Add some cheese and a dollop of guacamole. Finish with a sprinkling of the remaining coriander leaves. Tuck in!