Preheat a grill pan over high heat.
In a food processor combine onion, garlic and cayenne. Finely chop the mixture by pulsing.
Heat oil in a small pan over medium low heat. When oil is warm, stir herb and garlic mixture into oil and heat 3 to 5 minutes, then remove from heat. The oil will become infused with the flavor of the herbs and garlic. Transfer to a bowl and stir in vinegar and salt. Taste to adjust seasonings.
Cut chicken tenders into thirds and place in a shallow dish. Wash hands.
Spoon half of your chimichurri over the chicken and coat completely and evenly. Using tongs, transfer the bites to the hot grill and cook 2 or 3 minutes on each side. Transfer bites to a serving plate. Serve with party picks and reserved chimichurri sauce for dipping.