Preheat a grill pan over medium heat.
In a large pot over medium heat, stir together the lager, chili sauce, vinegar, brown sugar, curry powder and hot sauce. Cook until reduced by half, 3 to 5 minutes.
While the sauce is reducing, grill the sausages on the grill pan until browned and cooked through, turning every so often, about 12 minutes. Set aside.
Brush the onions with olive oil, season with salt and pepper and grill on the same pan you grilled the sausages. Cook until brown and golden, about 10 minutes.
Put the grilled sausages in the pot with the sauce, then add the onions. Cook together for 1 to 2 minutes.
Serve the sausages on crusty rolls topped with the onions and lots of sauce.