To make syrup, add orange juice, zest and Rooibos Syrup to a small, heavy-bottom saucepan. Bring to a boil, stirring occasionally until it thickens, about 20 minutes. Stir in butter, vanilla and salt. Set aside and keep warm.
Whisk together eggs and buttermilk, and put in a shallow pan (a rectangular baking dish works well). Add bread and turn to coat both sides with the egg mixture. Leave bread to soak for a few minutes to absorb mixture.
Heat a pan over medium heat, lightly coat with cooking oil spray. Fry bread until it’s golden brown on each side.
To serve, top French toast with syrup and a sprinkling of chopped walnuts.
Combine all ingredients in a medium saucepan. Over medium-high heat, stir until sugar and honey are dissolved. Bring to a boil. Reduce heat to medium, keeping the syrup at a boil, stirring occasionally until the syrup is reduced to 1 1/2 cups, about 45–60 minutes. Strain syrup with a wire-mesh strainer. It’s OK if some tea leaves remain in syrup.
Rooibos Syrup can be made a day ahead.