Heat the oil over medium heat in a frying pan for 1 minute. Add the onions and garlic and cook for about 5 minutes, stirring occasionally.
Increase the heat to medium-high and add the tinned tomatoes with their juices. Cook for about 10 minutes, stirring every minute or so, until the tomatoes dissolve into a thick sauce and the juices evaporate. If you’re not using a wide frying pan (e.g., if you’re using a tall saucepan), this may take longer.
Reduce heat to medium, add the dried mint, cayenne pepper, oregano, and salt, and cook for another 2 minutes to infuse everything with flavour.
Remove from heat, stir in the lemon juice, refrigerate, and serve either cold or at room temperature.