Put the mushrooms in a small bowl and add 1/2 cup of hot water to cover (if you need to add more - do so. Let the mushrooms soak for about 1/2 hour.
Remove mushrooms, reserving the water. Clean mushrooms to remove any grit and chop coarsely.
Filter the water through a paper towel placed in a sieve.
Heat oil and butter in a large skillet over medium high heat. When the butter has melted add the chicken and sauté on both sides for about 2-3 minutes per side.
Remove the chicken and add the onion to the pan. Cook onion until translucent (about 5 minutes) and then return the chicken to the pan.
Stir in mushrooms and their liquid. Combine the wine and the tomato paste. Add to the pan, cover and simmer for 20 minutes. Remove the chicken from the pan again, and raise the heat and reduce the sauce until it thickens (about 10 minutes).