Heat 2 tsp oil in a large non-stick frying pan. Add sausages. Cook, turning often, until evenly browned. Transfer to a plate lined with paper towel
Heat remaining 1 tbs oil in the pan over medium heat. Add onion. Cook, stirring often, for 4-5 minutes until soft
Stir in tomatoes and stock. Return sausages to pan. Stir to combine. Bring to the boil. Reduce heat and simmer, uncovered, for 20-25 minutes until sausages are cooked through.
Stir through spinach until just wilted. Season to taste. Serve with potato mash