In a mixing bowl, use a fork or a potato masher to mash the avocados to your desired consistency.
Add in the onions, jalapeño, cilantro, lime juice, salt, black pepper and mix until well combined. (If adding tomatoes, add them in the very end since they release moisture)
For Sandwich:
Grease a tawa over a medium flame. Toast the bread on both sides with some butter or oil till they become golden brown and crisp.
Place the toasted bread on a serving plate.
Spread 2-3 tablespoons of guacamole over the slice of bread and then cover with another slice of bread.
Cut it in half, Serve immediately with a cup of tea/coffee.
Notes
Note: Nutrition values are my best estimates. If you rely on them for your diet, use your preferred nutrition calculator.