Combine all the seasonings together in a small bowl. Press seasoning mixture all over rump roast.
Over medium-high heat, sear all sides of the seasoned rump roast. Then place in a large slow cooker with beef stock. Cook over low heat for 6-8 hours.
Fried Cucumbers
Slice cucumbers thinly, about ¼ inch thick. In a large skillet, toss cucumber in with 2 tbsp. of butter. Sauté cucumbers until brown. Flip and toss cucumber around to evenly cook.
While cucumbers are browning, make gravy in a small saucepan. Sauté 2 tbsp. butter with chopped onion. Add flour and cook on low heat for 1 minute. Add ½ cup beef stock from slow cooker. Cook on low for 5 minutes until gravy thickens.
After gravy thickens, pour into pan with cucumbers and let simmer for 5 minutes. Squeeze in lemon juice over cucumbers and serve under sliced slow cooked beef rump roast.