Heat oil in a large pan or skillet over medium-high heat. Add the chicken strips and fry for 3-4 minutes, stirring occasionally, until starting to brown.
Dice the onions and add them to the pan with the chicken. Cook for about 2 minutes, stirring.
Season with salt and pepper, then dust the flour over the mixture and stir well. Cook for about 2 minutes, stirring constantly.
Stir in the tomato paste.
Pour in the chicken broth and stir well. Simmer over medium heat for about 5 minutes until the chicken is cooked through (internal temperature 74°C / 165°F).
While the chicken simmers, cut the chives into rings and chop the green pepper.
Stir the crème fraîche and chopped green pepper into the pan. Bring back to a boil.