Heat a dash of oil in a large frying pan, and add the peppers, onion, broccoli, and mushrooms. Cook over a medium heat for 5 minutes, stirring regularly, until the vegetables are fairly soft, but still have a little bit of bite (the broccoli will probably still be quite crisp).
Add the garlic, artichokes and beans, and cook for a few more minutes, then remove from the heat. Add the pesto and cheddar cheese, and mix thoroughly. Season to taste.
Heat the oven to 190°C (Gas Mark 5 / 375°F).
To make the cheesy pesto crumb, use your fingertips to rub together the plain flour and butter in a mixing bowl. Stop when the mixture resembles breadcrumbs - you don't want it to come together into a ball (it doesn't matter if it's not perfectly mixed - don't overwork it). Add the oats, grated cheese, and pesto, along with a pinch of salt and pepper. Use a fork to mix everything together - again, it doesn't matter if it's not perfect, just try to mix the pesto through as best as you can.
Transfer the vegetables to a baking dish, and top with the cheesy crumble mixture. Bake for around 30 minutes, or until the topping is golden brown and crispy. Serve topped with fresh parsley, if desired.