Take a pan, add in the chicken breasts, water and salt together, and heat it on a medium-high flame. Bring this to a boil, then reduce the heat to and let it simmer and cook for 20-30 minutes, till the chicken is soft and cooked.
Once cooked, remove the chicken and reserve the stock. Let the chicken cool, then shred it with your fingers.
Take a saucepan, add oil and heat it. Saute and cook the onion for 2-3 minutes till they turn transparent in colour. Next, add the tomato and cook for another 2-3 minutes.
Now, add the shredded chicken, salt and pepper and let it simmer and cook. Then remove the pan from the heat, stir in the cream cheese and adjust the seasoning as per taste.
In a separate pan, pour in 2 cups of the reserved chicken stock along with the flour, oil, salt and pepper. Stir this mixture together till it is smooth.
Put this pan on a medium flame and cook while stirring constantly till the batter becomes smooth and easily pulls away from the sides of the pan. Now let this dough and the chicken filling cool down for an hour or so.
After this time period, take a golf ball-sized dough and flatten it into a small circle. Place 1 tablespoon of this chicken filling in the middle and bring the sides of the dough up to close the filling.
Shape this dough into a little drumstick. Repeat this process with the remaining doughs and filling.
Once done, take a coxinha and dip it in the beaten egg bowl and let the excess egg drip off. Roll it in the breadcrumbs and set it on a baking sheet. Repeat this process with the remaining coxinhas.
Deep fry these chicken coxinhas till they turn into a beautiful golden brown colour.
Serve hot for best taste.