Cube beef into 2 inch by 2-inch chunks. Alternate 1/2 pound of beef cubes with 1/4 onion and bell pepper onto a wooden skewer. Repeat process until 4 kabobs are skewered. Place kabobs in shallow pan and make marinade.
In a bowl, whip together mustard, garlic, vinegar, and season with salt and black pepper.
Slowly pour in LouAna Peanut Oil while whipping constantly until all of the oil is incorporated. Reserve a small amount of dressing for later use.
Coat beef kabobs with dressing, refrigerate and allow kabobs to marinate two hours up to overnight.
Fire up BBQ pit or gas grill and grill kabobs to desired doneness. Coat tomato slices with remaining dressing and towards end of cooking process grill tomatoes until just heated.
For sauce, heat 2 teaspoons of LouAna Peanut Oil , add garlic and cook over medium low heat until garlic is browned but not burnt. Add broth and tarragon. Bring to boil, reduce heat and simmer until the broth is reduced by half.
Lower fire as low as it will go and swirl in fresh tarragon and butter. Simmer until butter is melted. Top beef kabobs with sauce and garnish with grilled tomato slices.