Combine both mustards, honey, lemon juice, rosemary, salt and pepper in a large bowl. Add chicken tenderloins to bowl and toss to combine. Place into the refrigerator to marinate for at least 30 minutes or overnight.

Heat olive oil in large pan over medium heat. Once hot, add chicken to the pan in a single layer, reserve the marinade. Depending on the size of your pan, you may need to cook chicken in 2 separate batches and clean pan in between. Cook chicken for 3 minutes. Once it's golden, flip the chicken and add the marinade into the pan so the sauce can heat up. Cook for 3 more minutes, or until chicken is cooked through. The sauce should become hot and bubbly.

Transfer to a serving dish and let cool 5 minutes before serving.