Place the unsweetened chocolate in a heatproof bowl and melt over a saucepan of simmering water. Whisk in sugar substitute and thin with the hot water and heavy cream. Whisk to blend thoroughly. Remove from heat, spread on a plate, and place in the freezer for about 10 minutes. Cut into small chunks after chilling.
While the chocolate is chilling, make the cannoli cream. With an electric mixer on high, whip heavy cream just until frothy, and then add sugar substitute and almond and vanilla extracts. Continue to whip on high until stiff peaks form. Be careful not to over-whip, or cream will break.
Gently fold in the ricotta cheese and almost all of the chilled chocolate chunks, saving a few chips for garnish. Spoon cannoli cream into parfait glasses, top with remaining chocolate chips, and refrigerate for at least 1 hour before serving.