Heat 1 tablespoon of oil in a large skillet over medium heat.
While the oil is heating up, sprinkle the salt, pepper, and marjoram onto each side of the chicken breasts.
Place the chicken into the hot skillet and cook until no longer pink - about 8 minutes on each side. (I like to use my Thermoworks Instant Read Thermometer to check doneness. When it reads 165℉ it's cooked through)
Once the chicken is cooked through, remove it from the pan and set it aside.
Add in the onion to the pan and cook until translucent, scraping up the bits from the bottom of the pan. It's Okay to add another tablespoon of oil into the pan if needed.
Once the onion is translucent, add the jalepeño and garlic and sauté for 3 more minutes.
Turn the heat to low, and add in the balsamic vinegar, water, and raspberry jam.
Gently stir the mixture until the raspberry jam has melted down and has formed a sauce with the vinegar.