Heat oil on medium flame in a saucepan and add mustard seeds.
Once the mustard seed splutters, add the curry leaves, red chillies, chopped onion, grated garlic, and ginger.
Sautée until the onions turn translucent and the garlic and ginger are softened.
Next, add chopped tomatoes, chilli powder, 5 spice, ground cumin, ground coriander, vinegar, sugar, and salt to taste.
Let this combination simmer on medium-low for about 30 minutes, stirring occasionally until it is thickened.
Remove from heat, and let it cool.
Sandwich:
Butter 2 slices of bread on one side.
Place one slice with the buttered side on a pan, and set it on medium heat.
Spread the chutney on the other side then sprinkle some chopped onion and a generous amount of both types of cheese.
Place the other slice of bread on top, with the buttered side facing away from the chutney.
Heat sandwich on pan, and cook for about 3 – 4 minutes on each side until the bread is crispy on both sides, and the cheese has completely melted on the inside.