Preheat oven to 180C/160C fan-forced. Grease a 16cm x 26cm slice tin with olive oil or oil of your choice. Line the base and sides with baking paper.
In a food processor place the dry ingredients and pulse to combine. Add the coconut oil and pulse again until combined and a wet dough is formed.
Press the mixture into the base of prepared pan. Bake for 15 to 17 minutes or until golden. Set aside to cool completely.
Place the cornflour and Natvia in a heavy-based saucepan. Gradually stir in lemon juice and coconut milk. Using a pinch of turmeric to tint the mixture pale yellow. Place over medium heat. Stir for 1 to 2 minutes or until Natvia dissolves. Increase heat to medium-high. Cook, stirring constantly for 5 minutes or until mixture just bubbles and thickens.
Working quickly, spoon over the base in the pan. Smooth the top. Refrigerate for 2 hours or until set.