Preheat the oven to 425°F for 15 minutes. Time will vary depending on your oven brand.
Place the sugar in a small bowl. Lay the vanilla bean flat. Look for the rougher, matte side – this is where the bean naturally splits open and where you want to cut. Hold the tip of the bean down with your finger. Using the sharp tip of a paring knife, carefully cut lengthwise down the center of the bean, following the matte side. Don't cut all the way through! Leave the end intact so the bean unfolds like a book.
Use the blunt back of the paring knife to scrape the fragrant vanilla bean seeds from the bean gently. Place the vanilla bean seeds into the small bowl with the sugar. Use your fingers to rub the vanilla seeds into the sugar until they are distributed throughout the sugar.
If you don't use all the sugar, use the remaining sugar for another recipe.
Combine the chopped strawberries, lemon juice and lemon zest, 1/2 cup of the vanilla sugar and salt in a large bowl. With a large spoon gently mix all the ingredients together. Spread the mixture on a half-sheet pan and place in the oven.
After the first 15 minutes, taste the mixture (careful it's hot) and add more sugar 1/4 cup at a time stirring after each addition. Continue to roas the strawberries, stirring them every 10 minutes until the strawberry syrup starts to thicken and bubble at the edge of the pans.
When done, remove them from the oven and use a large heatproof spatula to scrape them into a large bowl. Allow the berries to cool until room temperature. Once cooled the berries can be used immediately or refrigerated up to two weeks.