Cut the chicken thighs into chunks - about 1.5in and then set aside.
Make the marinade. Strip the leaves from the tarragon and place them in a mortar with the roughly chopped chili. Add the garlic, a generous pinch of salt, a grinding of pepper and pound everything to a paste with a pestle (alternatively use a food processor).
Stir in 1 teaspoon of smoked pimenton (this adds a lovely smoky flavour to the marinade). Add the tomato paste, balsamic vinegar and olive oil. Stir thoroughly and pour over the chicken. Leave the chicken to marinate until ready to cook.
Preheat the grill. Thread the chicken pieces onto skewers and cook the chicken for 4-5 minutes on each side, until golden and cooked through. Serve immediately.