- Melt butter in a large heavy-based saucepan over medium-low heat. Add the onion and cook, stirring, for 5 mins or until onion softens. Add the capsicum and cook, stirring, for 5 mins or until almost tender. Add the cumin, coriander and mustard powder. Cook, stirring, for 30 secs or until aromatic.
- Add rice and stir to combine. Stir in the stock. Increase heat to medium-high and bring to the boil. Reduce heat to low. Cover and cook for 30 mins or until the liquid is absorbed and the rice is tender. Set aside, covered, for 5 mins to steam. Use a fork to separate the grains.
- Add the corn, black beans, cheddar and jalapeño, if using, to the rice mixture and stir to combine. Season. Place the tortillas on a clean work surface. Divide the rice mixture evenly among the tortillas. Fold in the edges and roll up to enclose the filling.
- Use a fork to mash the avocado, sour cream and lemon juice in a small bowl. Stir in the coriander. Season.
- Cut the tortillas in half. Serve with the guacamole.
Serve with lime wedges and coriander sprigs