Slice the avocado into halves lengthwise. Use a spoon or avocado tool to remove and discard the seed. Next, scoop out the avocado and place it in a bowl.
Add salt, ground black pepper, crushed red pepper flakes, and lemon juice to the bowl. Use the back of a fork to mash the avocado and combine it with the herbs and spices and lemon juice.
Toast the bread in a toaster or toast the bread in a skillet or grill pan. To use a skillet or grill pan: Coat the inside of the pan with nonstick cooking spray, brush both sides of each bread slice with olive oil or spread the sides with butter. Cook the bread for 2 to 3 minutes on each side, until the bread is lightly toasted and golden brown. Use heat-resistant tongs to remove the bread from the pan.
Spread the mashed avocado over the toasted bread slices. Add extra toppings, such as sliced tomatoes or radishes, poached eggs, smoked salmon, and crumbled feta cheese. Everything bagel seasoning also makes a great topping for avocado toast.
Serve the avocado toast right away. Great side dishes for avocado toast include muffins, granola, yogurt, and fresh fruit.