In a large frying pan, heat olive oil on medium high heat. Add tomato, scallions, garlic and green chili. Cook for about 3-4 minutes until mixture has softened. Add salt and cumin, stir to combine. Add entire can of tuna (including the olive oil from the can. Mix to incorporate everything together. You may have to break up the tuna into small chunks. Cook about another 3 minutes, to heat the tuna through.
Remove from heat, add the chopped cilantro and squeeze the lemon over and gently mix everything together.
Top toasted bread slices with avocado and tuna mixture.