Peel and finely dice the onion and carrot to a uniform size of about 1 cm, then continue with dicing the celery and red pepper to a similar size.
Heat the olive oil in a large saucepan on a low-medium heat. Add the onion and cook for 5 minutes.
Add the other vegetables and continue to cook for 20-25 minutes, stirring occasionally so they don’t catch. If they are cooking too quickly then turn the heat right down. The vegetables are ready when they are soft and turning translucent.
Meanwhile pre-heat the oven to 190°C / 170°C fan assisted / gas mark 5 / 375°F and line a large baking tray with baking parchment.
Remove the vegetables from the heat and allow to cool.
Whisk together the breadcrumbs, milk and eggs in a large mixing bowl.
Add the mince along with the rest of the ingredients (but only half of the BBQ sauce – leaving the rest for glazing) and mix everything together until combined and the mince mixture is completely cohesive.
Tip the mixture carefully into the centre of the baking tray and shape with clean hands into a large loaf shape.
Brush the surface of the whole loaf with the rest of the BBQ sauce.
Place the baking tray in the oven and bake the meatloaf for 50 minutes.
Remove the meatloaf from the oven and allow to rest for 15-20 minutes for the meatloaf to settle and firm up before cutting into slices and serving.